voucher.rb

class Voucher < ActiveRecord::Base
   has_and_belongs_to_many :users, :join_table => :voucher_users
   belongs_to :plan

  def self.create_for_beta_user(user)
    voucher = new
    voucher.code = [4,4,4,4].map {|x| random_string(x) }.join("-")
    voucher.expires_on = 2.months.from_now
    voucher.price = 19
    voucher.plan = Plan.premium
    voucher.referrer = user.username
    voucher.times_usable = 5
    voucher.save!
    voucher
  end

  def self.random_string(len = 4)
    # The argument n specifies the length of the random length. The length of the result string is twice of n.
    ActiveSupport::SecureRandom.hex(len/2)
  end

  def usable_by?(user)
    usable? && !used_by?(user)
  end

  def used_by?(user)
    !!users.find_by_id(user.id)
  end

  def usable?
    (not expired?) and times_usable > 0
  end

  def expired?
    expires_on.present? && expires_on < Time.now
  end

  def merchant_reference(user_id = self.user_id)
    now = Time.now
    [user_id, now.month, now.year, plan_length_type].join("-")
  end

  # use the voucher.
  def use!(user)
    users << user
    self.decrement!(:times_usable)
  end

end